It is well known that ellipsometer and polarimeter systems allow determination of sample system physical and optical properties, (such as thickness, refractive index and extinction coefficient of surface films thereon), by detecting changein "Polarization State" and/or Intensity of a beam of polarized light which is caused to interact with said sample system, where Polarization State here refers to a set of values for Polarized Light Beam Orthogonal Components, (such as "S" and "P"), Magnitude Ratio, and a Phase Angle therebetween. (It is noted that "P" refers to that component which is in a plane containing the normal to a sample system and incident and/or transmitted beam(s) of polarized light, and "S" refers to that component perpendicular thereto and parallel to the surface of said sample system. It is also noted that a "full" polarization state also requires designation of an absolute value to which a magnitude ratio is referenced, and the direction of rotation of a polarized beam of light).
It is also noted that while ellipsometer and polarimeter systems are finding increased application in vacuum systems which are utilized in material deposition and etching, (to mediate sample system monitoring and process control), many such applications involve retrofitting an ellipsometer or polarimeter system to a vacuum system which has component geometry that makes it difficult to direct an electromagnetic beam from a source thereof such that it interacts with a sample system within a vacuum chamber. In particular, sample system containing vacuum chambers often have, for instance, complex sputtering or electron beam source means and robotics means present therewithin, which an ellipsometer or polarimeter electromagnetic beam must circumvent to arrive at a sample system therewithin.
Continuing, as general background, it should be appreciated that ellipsometer systems can be broadly classified as:
1. Rotatable Element or Intensity Modulating Rotating Element Ellipsometers (REE); and PA1 2. Phase Modulating Modulation Element Ellipsometers (MEE). PA1 a. that each of said first and second electromagnetic beam directing means are made of a material with refractive properties such that when the angle of incidence of said spectroscopic polarized beam of electromagnetic radiation which reflects from the third side thereof, with respect to a normal to said third side is nominally fifty-two (52) degrees, the angle of incidence of said spectroscopic polarized beam of electromagnetic radiation with respect to a normal to a surface of said sample system is less than seventy (70) degrees, and PA1 b. when the angle of incidence of said spectroscopic polarized beam of electromagnetic radiation which reflects from the third side of each said first or second electromagnetic beam directing means is varied by plus or minus one (1) degree around said nominal fifty-two (52) degrees, the retardation entered between orthogonal components in said spectroscopic polarized beam of electromagnetic radiation varies by, on the order of one (1) degree at any wavelength between two-hundred-fifty (250) and seven-hundred-fifty (750) nanometers. PA1 a. that each of said first and second electromagnetic beam directing means are made of fused quartz which demonstrates refractive properties such that the angle of incidence of said spectroscopic polarized beam of electromagnetic radiation which reflects from the third side thereof, with respect to a normal to said third side, is nominally fifty-two (52) degrees when said angle of incidence of said spectroscopic polarized beam of electromagnetic radiation with respect to a normal to a surface of said sample system is nominally sixty-nine (69) degrees, and PA1 b. that each said first and second electromagnetic beam directing means cause, in use, a change in ellipsometric DELTA phase angle between orthogonal components in said spectroscopic polarized beam of electromagnetic radiation which reflects from the third side of each of said first and second electromagnetic beam directing means which is within the range of approximately forty-six (46) to thirty-nine (39) degrees for wavelengths within the respective range of approximately two-hundred-fifty (250) to seven-hundred-fifty (750) nanometers; and PA1 c. that when the angle of incidence of said spectroscopic polarized beam of electromagnetic radiation which reflects from the third side of each said first or second electromagnetic beam directing means is varied by plus or minus one (1) degree around said nominal fifty-two (52) degrees, the retardation entered between orthogonal components in said spectroscopic polarized beam of electromagnetic radiation varies by, on the order of one (1) degree at any wavelength between two-hundred-fifty (250) and seven-hundred-fifty (750) nanometers. PA1 1. providing an ellipsometer/polarimeter system as described infra herein; PA1 2. placing a sample system so that it is held in place at said stage for holding a sample system; PA1 3. causing said source of a polarized spectroscopic beam of electromagnetic radiation to emit a polarized spectroscopic beam of electromagnetic radiation; PA1 4. receiving said beam of spectroscopic polarized radiation in said detector after it has interacted with said first electromagnetic beam directing means, said stage for holding a sample system and said second electromagnetic beam directing means;
An example, for instance, is presented in a Patent to Woollam et al., U.S. Pat. No. 5,373,359, which describes a Rotating Analyzer Ellipsometer (RAE) in which a Light Source provided beam of light is caused to pass through a Polarizer, (which serves to set a Polarization State therein), then interact with a sample system. Said interaction with said sample system serves to alter the Polarization State of said polarized beam of light, which polarized beam of light then sequentially encounters a Rotating Analyzer and a Dispersion Optics, (eg. a Diffraction Grating is specified), which forms therefrom a multiplicity of essentially single wavelength polarized beams of light. Said multiplicity of essentially single wavelength polarized beams of light are then caused to enter a Photo Detector Array, in which Photo Detector Array, individual Detector Elements serve to develop a representative signal for each. Fourier Analysis, for instance, of said signals allows determination of parameters which allow determination of sample system characterizing PSI and DELTA values. It is noted that in said Woollam et al. (RAE) there is no additional focusing applied after the polarized beam of light encounters the sample system. Additional Patents to Johs et al. and Green et al., U.S. Pat. Nos. 5,504,582 and 5,521,706 respectively provide further insight into rotating analyzer ellipsometer systems.
Another U.S. Pat. No. 5,416,588 to Ducharme et al., describes a Modulation Element Ellipsometer (MEE) comprised of a Light Source, a Polarizer, a Polarization State Modulator Element, a means for splitting Orthogonal Components in a Beam of Polarized Light after interaction with a sample system, two Detector Elements and an Analysis system. In use a beam of light is provided by the Light Source and a state of Polarization is set therein by said Polarizer, after which the polarized beam of light is subjected to a Polarization State Modulation and caused to interact with a sample system, which sample system changes the State of Polarization of said Phase Modulated Polarized beam of light. Orthogonal Components of said Polarized beam of Light are then isolated and subjected to separate, for instance, Fourier Analysis. Appropriate utilization of the Coefficients of the terms of a Fourier Series allows determination of sample system characterizing PSI and DELTA values. It is noted the described Modulation Element Ellipsometer (MEE) utilizes Coefficients from Fourier Series based upon both Orthogonal Components. Some Modulation Ellipsometers utilize Fourier Series Coefficients from only one such Orthogonal Component. While the specifics of signal generation are different in (REE) and (MEE) ellipsometers, and even amongst Ellipsometers of similar type, the end result of utilization thereof is provision of PSI and DELTA values for sample systems analyzed therein.
Another U.S. Pat. No. 5,706,087 to Thompson et al. describes a system for changing the direction of a beam of electromagnetic radiation so that sample systems which can not be easily situated on a sample system supporting stage in an ellipsometer or polarimeter or the like system can be investigated without reconfiguration. Said system comprises an electromagnetic beam directing means which is easily mounted to said sample system supporting stage.
Another Patent to Woollam et al., U.S. Pat. No. 5,582,646, describes a method and system for allowing investigation of sample systems utilizing a spectroscopic electromagnetic beam which is caused to impinge on a sample system at an angle greatly in excess of the Brewster Angle, (which is nominally seventy-five (75) degrees for semiconductors). Said 646 Patent identifies certain wavelengths in a spectroscopic range of wavelengths in which ellipsometric DELTA sensitivity to changes in an investigated sample system is sufficiently high to detect small changes in an investigated sample system. Said 646 Patent system finds application in vacuum deposition, (eg. MBE), systems which are provided with ports to which RHEED systems are normally connected, which ports provide for glancing angles of incidence of electrons, (eg. eighty-five (85) degrees), caused to impinge thereupon. Rather than connect a RHEED system, an ellipsometer system can be connected at the RHEED port and an electromagnetic beam be caused to impinge on said sample system at said glancing angles of incidence of electrons, (eg. eighty-five (85) degrees). While this greatly diminishes DELTA sensitivity to changes in sample system at most wavelengths, it is found that when appropriate wavelengths are monitored, DELTA sensitivity remains high.
A system which allows use of electromagnetic beams caused to impinge upon a sample at less than a Brewster Angle is identified in co-pending patent application Ser. No. 09/033,694. Said 694 Application describes a system wherein a beam of electromagnetic radiation can be made to impinge upon a sample system at an angle-of-incidence which is below, (eg. 65 degrees), a typical Brewster Angle, which Brewster angle is, again, near seventy-five (75) degrees in most semiconductors. A typical range of angle-of-incidence over which the said invention can be applied, however, is between thirty (30) and eighty (80) degrees from a normal to a sample system surface, with a range of deviation from a Brewster angle of between five (5) and ten (10) degrees being of particular relevance. It is noted that the present invention provides convenient means by which to achieve a smaller electromagnetic beam "Spot" size, (which accompanies a smaller angle-of-incidence on an investigated material system). The present invention also enables realization of laterally-compact ellipsometer or polarimeter and the like systems.
Generally, the present invention can be applied to essentially any ellipsometer or polarimeter and the like system, and provides a solution to a problem in the use thereof which presents when a sample system is to be investigated with a polarized beam of electromagnetic radiation which is initially oriented in a propagation direction other than appropriate to cause it to impinge upon a sample system, and in which space constraints prevent reorienting the source of the initially oriented polarized beam of electromagnetic radiation. The present invention provides the primary benefit of maintaining both ellipsometric PSI and ellipsometric DELTA sensitivity to changes in investigated sample systems while changing said electromagnetic beam propagation direction.
With an eye to the present invention, a Search of Patents was conducted, with the result being that very little was found. A Patent to Kasai, U.S. Pat. No. 3,874,797 is disclosed, however, as it describes a system for directing an electromagnetic beam utilizing totally reflecting prisms. As well, a Patent to Lange, U. S. Pat. No. 4,801,798 is disclosed as it describes a system which utilizes electromagnetic beam directing reflective means in a system which causes an electromagnetic beam to impinge upon an investigated sample system at an angle very near to a perpendicular to a surface thereof. A Patent to Smith, U.S. Pat. No. 4,381,151 is also disclosed as it describes a system in which numerous reflections of a light beam occur.
A paper titled "Division-Of-Amplitude Photopolarimeter Based on Conical Diffraction For a Metallic Grating" by Azzam, in Applied Optics, Vol. 31, No. 19, Jul. 1, 1992 and U.S. Pat. No. 5,337,146 are also noted. While the system described in said references is somewhat relevant, the purpose of the System and Method of Use described in said references is to allow simultaneous measurement of all four Stokes Parameters of a Beam of Light.
A particularly relevant paper is titled "In Situ Spectroscopic Ellipsometry For Advanced Process Control In Vertical Furnaces", Lehnert et al., Thin Solid Films, 313-314 (1998). Said paper describes means for directing an initially vertically oriented beam of electromagnetic radiation onto a sample system at an angle of between seventy (70) to seventy-five (75) degrees, said means being prisms positioned in a vertically oriented furnace. While this paper describes a system which is observably physically similar to that of the present invention, it does not suggest use of said described system where electromagnetic beams are caused to approach sample systems at angles of incidence below seventy (70) degrees, nor does it provide insight as how to maintain high ellipsometric parameter (ie. PSI and/or DELTA), sensitivity to sample system changes where a beam of electromagnetic radiation is caused to approach a surface of a sample system at an angle-of-incidence significantly less than a Brewster Angle, (ie. less than seventy (70) degrees).
Also, a reference titled "ELLIPSOMETRY AND POLARIZED LIGHT", by Azzam and Bashara, North-Holland, 1977, is incorporated by reference into this Disclosure for the purpose of providing general information regarding sample analysis systems utilizing electromagnetic beams, ellipsometry, polarimetry and fundamentals of electromagnetic beams.
Finally, a paper by Johs titled "Regression Calibration Method For Rotating Element Ellipsometers", Thin Solid Films, 234 (1993), is identified and incorporated by reference into this Disclosure for the purpose of providing general information regarding the use of regression in parameter evaluation in sample analysis systems which utilize electromagnetic beams.
In view of known prior art, it is apparent that a system, and method of its use, which would allow a user of a sample analysis system such as a ellipsometer, polarimeter or a functionally similar system, to investigate sample systems with beams of electromagnetic radiation which are not initially oriented in a propagation direction appropriate to effect interaction with a sample system at below Brewster angles-of-incidence with respect to a normal to a material system surface, without requiring major system reconfiguration procedures be performed, which system and method allow changing the propagation direction of an initial beam of electromagnetic radiation without greatly diminishing the sensitivity of either ellipsometric (PSI) and (DELTA) parameters to changes investigated sample system surface properties, would be of great utility. In particular, such a system, and method of use, would find application in directing electromagnetic beams in vacuum chambers which contain, for instance, complex sputtering or electron beam source means and robotics means present therewithin, which an ellipsometer or polarimeter electromagnetic beam must circumvent to arrive at a present sample system. The present invention provides such a system and method of its use.